Can genes influencing muscle function affect the therapeutic response to enzyme replacement therapy (ERT) in late-onset type II glycogenosis?

Six-Minute Walk Distance Is a Useful Outcome Measure to Detect Motor Decline in Treated Late-Onset Pompe Disease Patients

Late-onset Pompe disease (LOPD) is a rare, progressive disorder characterized by limb–girdle muscle weakness and/or respiratory insufficiency, caused by acid alpha-glucosidase (GAA) gene mutations and treated with enzyme replacement therapy. We studied isometric muscle strength in eight muscle groups bilaterally using a Biodex® dynamometer, as well as the Medical Research Council sum score (MRC-SS), hand grip strength, 6 min walk distance (6MWD), 10 m walk test (10MWT) and timed up-and-go test (TUG) in 12 adult, ambulatory, treated LOPD patients and 12 age-/gender-matched healthy controls, every 6 months for 2 years. The mean isometric muscle strength showed a significant decline in right and left knee extensors at 12 months in controls (p < 0.014; p < 0.016), at 18 months in patients (p < 0.010; p < 0.007) and controls (only right side, p < 0.030) and at 24 months in both groups (p < 0.035). The mean 6MWD in patients significantly decreased after 24 months, from 451.9 m to 368.1 m (p < 0.003), whereas in controls, the mean 6MWD significantly increased after 6 months (p < 0.045) and 18 months (p < 0.020) (at 24 months p = 0.054). In patients and controls, the MRC-SS, hand grip test, 10MWT and TUG did not show significant changes (p > 0.05). We conclude that the 6MWD is a useful outcome measure to detect motor decline in treated LOPD patients.

Polymorphism in exercise genes and respiratory function in late-onset Pompe disease

Genetic polymorphisms influencing muscle structure and metabolism may affect the phenotype of metabolic myopathies. We here analyze the possible influence of a wide panel of "exercise genes" on the severity and progression of respiratory dysfunction in late-onset Pompe disease (LOPD). We stratified patients with comparable age and disease duration according to the severity of their respiratory phenotype, assessed by both upright FVC% and postural drop in FVC%. We included 43 patients with LOPD (25 males, age 50.8 ± 13.6 yr) with a 2-yr follow-up since the beginning of enzyme replacement therapy (ERT). Twenty-two patients showed a postural drop >25% T0, seven other patients developed it during the follow-up. We analyzed the relationship between the progression of respiratory dysfunction and genetic polymorphisms affecting muscle function and structure [angiotensin converting enzyme (ACE), α-actinin 3 (ACTN3), peroxisome proliferator-activated receptor α (PPR-α), angiotensin (AGT)], glycogen metabolism [glycogen synthase (GYS), glycogen synthase kinase-3 isoform β (GSK3β)], and autophagy [sirtuin 1 (SIRT1), autophagy-related gene 7 (ATG7)]. Individuals carrying two copies of the ACE D-allele shared a 24-fold increase in the risk of severe respiratory dysfunction and progression during the 2-yr follow-up. ACTN3-XX polymorphism was also associated with worse respiratory outcome. The study of exercise genes is of particular interest in respiratory muscles, due to their peculiar features, that is, continuous, low-intensity contraction and prominent recruitment of type I fibers. In line with previous observations on skeletal muscles, ACE-DD and ACTN3-XX genotypes were associated with indirect evidence of more severe respiratory phenotypes. On the contrary, polymorphisms related to autophagy and glycogen metabolism did not seem to influence respiratory muscles.NEW & NOTEWORTHY Previous reports evaluated the role of exercise genes in influencing skeletal muscle phenotype and response to ERT in LOPD. Here, we investigate the role of polymorphisms in several exercise gene, focusing on respiratory muscles. ACE-DD and ACTN3-XX polymorphisms, possibly influencing muscle properties and fiber composition, were associated with more severe respiratory phenotypes.

A Systematic Review and Meta-Analysis of Enzyme Replacement Therapy in Late-Onset Pompe Disease

Pompe disease (PD) is a glycogen storage disorder caused by deficient activity of acid alpha-glucosidase (GAA). We sought to review the latest available evidence on the safety and efficacy of recombinant human GAA enzyme replacement therapy (ERT) for late-onset PD (LOPD).

METHODS

We systematically searched the MEDLINE (via PubMed), Embase, and Cochrane databases for prospective clinical studies evaluating ERT for LOPD on pre-specified outcomes. A meta-analysis was also performed.

RESULTS

Of 1601 articles identified, 22 were included. Studies were heterogeneous and with very low certainty of evidence for most outcomes. The following outcomes showed improvements associated with GAA ERT, over a mean follow-up of 32.5 months: distance walked in the 6-min walking test (6MWT) (mean change 35.7 m (95% confidence interval [CI] 7.78, 63.75)), physical domain of the SF-36 quality of life (QOL) questionnaire (mean change 1.96 (95% CI 0.33, 3.59)), and time on ventilation (TOV) (mean change -2.64 h (95% CI -5.28, 0.00)). There were no differences between the pre- and post-ERT period for functional vital capacity (FVC), Walton and Gardner-Medwin Scale score, upper-limb strength, or total SF-36 QOL score. Adverse events (AEs) after ERT were mild in most cases.

CONCLUSION

Considering the limitations imposed by the rarity of PD, our data suggest that GAA ERT improves 6MWT, physical QOL, and TOV in LOPD patients. ERT was safe in the studied population. PROSPERO register: 135102.

Using human Pompe disease-induced pluripotent stem cell-derived neural cells to identify compounds with therapeutic potential

Pompe disease (OMIM # 232300) is a glycogen storage disease caused by autosomal recessive mutations of the gene encoding alpha-1,4-glucosidase (GAA; EC 3.2.1.20). Despite the relatively effective employment of enzyme replacement therapy, some critical medical issues still exist in patients with this disease, including the persistence of abnormalities in the central nervous system (CNS), probably because of the inability of the recombinant GAA to pass through the blood-brain barrier. To address this issue, identification of more therapeutic agents that target the CNS of patients with Pompe disease may be required. In this study, we derived neuronal cells from Pompe disease-induced pluripotent stem cells (Pom-iPSCs) and proved that they are able to recapitulate the hallmark cellular and biochemical phenotypes of Pompe disease. Using the Pom-iPSC-derived neurons as an in vitro drug-testing model, we then identified three compounds, ebselen, wortmannin and PX-866, with therapeutic potential to alleviate Pompe disease-associated pathological phenotypes in the neurons derived from Pom-iPSCs. We confirmed that all three compounds were able to enhance the GAA activity in the Pom-iPSC-derived neurons. Moreover, they were able to enhance the GAA activity in several important internal organs of GAA-deficient mice when co-injected with recombinant human GAA, and we found that intraperitoneal injection of ebselen was able to promote the GAA activity of the GAA-heterozygous mouse brain. Our results prove the usefulness of Pom-iPSC-derived neuronal populations for identifying new compounds with therapeutic potential.

Molecular genetics of Pompe disease: a comprehensive overview

Pompe disease (PD) is an autosomal recessive lysosomal disorder caused by the deficient activity of acid alpha-glucosidase (GAA) enzyme due to mutations in the GAA gene. The enzymatic deficiency leads to the accumulation of glycogen within the lysosomes. Clinically, the disease has been classically classified in infantile and childhood/adult forms. The GAA gene has been localized to chromosome 17q25.2-q25.3 and to date, 582 mutations distributed throughout the whole gene have been reported (HGMD: http://www.hgmd.cf.ac.uk/ac/). All types of mutations have been described; missense variants are the most frequent type followed by small deletions. Most GAA mutations are private or found in a small number of families. However, an exception is represented by the c.-32-13T>G splice mutation that is very common in patients of Caucasian origin affected by the childhood/adult form of the disease, with an allelic frequency ranging from 40% to 70%. In this article, we review the spectrum of GAA mutations, their distribution in different populations, and their classification according to their impact on GAA splicing process, protein expression and activity. In addition, whenever possible, we discuss the phenotype/genotype correlation. The information collected in this review provides an overview of the molecular genetics of PD and can be used to facilitate diagnosis and genetic counseling of families affected by this disorder.

The ACE I/D polymorphism does not explain heterogeneity of natural course and response to enzyme replacement therapy in Pompe disease

The majority of children and adults with Pompe disease in the population of European descent carry the leaky splicing GAA variant c.-32-13T>G (IVS1) in combination with a fully deleterious GAA variant on the second allele. The phenotypic spectrum of this patient group is exceptionally broad, with symptom onset ranging from early infancy to late adulthood. In addition, the response to enzyme replacement therapy (ERT) varies between patients. The insertion/deletion (I/D) polymorphism of the angiotensin I-converting enzyme (ACE) has been suggested to be a modifier of disease onset and/or response to ERT. Here, we have investigated the effect of the ACE I/D polymorphism in a relatively large cohort of 131 children and adults with Pompe disease, of whom 112 were followed during treatment with ERT for 5 years. We assessed the use of wheelchair and mechanical ventilation, muscle strength assessed via manual muscle testing and hand-held dynamometry (HHD), distance walked on the six-minute walk test (6MWT), forced vital capacity (FVC) in sitting and supine position and daily-life activities assessed by R-PAct. Cross sectional analysis at first visit showed no differences between the genotypes with respect to age at first symptoms, diagnosis, wheelchair use, or ventilator use. Also response to ERT over 5 years assessed by linear mixed model analyses showed no significant differences between ACE groups for any of the outcome measures. The patient cohort contained 24 families with 54 siblings. Differences in ACE genotype could neither explain inter nor intra familial differences. We conclude that the ACE I/D polymorphism does not explain the large variation in disease severity and response to ERT observed among Pompe patients with the same c.-32-13T>G GAA variant.

Long-term follow-up of 17 patients with childhood Pompe disease treated with enzyme replacement therapy

OBJECTIVES

Pompe disease is a progressive metabolic myopathy for which enzyme replacement therapy (ERT) was approved in 2006. While various publications have examined the effects of ERT in classic-infantile patients and in adults, little has been published on ERT in children with non-classic presentations.

STUDY DESIGN

This prospective study was conducted from June 1999 to May 2015. Seventeen patients from various countries participated. Outcome measures comprised muscle function (6-minute walk test, quick motor-function test (QMFT)), muscle strength (hand-held dynamometry; manual muscle testing), and lung function (FVC sitting and supine). For each outcome measure, we used linear mixed-effects models to calculate the difference at group level between the start of therapy and 7 years of ERT. Patients' individual responses over time were also evaluated.

RESULTS

Eleven males and six females started ERT at ages between 1.1 and 16.4 years (median 11.9 years); 82% of them carried the common c.-32-13T > G GAA gene variant on one allele. At group level, distance walked increased by 7.4 percentage points (p < 0.001) and QMFT scores increased by 9.2 percentage points (p = 0.006). Muscle strength scores seemed to remain stable. Results on lung function were more variable. Patients' individual data show that the proportion of patients who stabilized or improved during treatment ranged between 56 and 69% for lung function outcomes and between 71 and 93% for muscle strength and muscle function outcomes.

CONCLUSIONS

We report a positive effect of ERT in patients with childhood Pompe disease at group level. For some patients, new or personalized treatments should be considered.

European consensus for starting and stopping enzyme replacement therapy in adult patients with Pompe disease: a 10-year experience

BACKGROUND AND PURPOSE

Pompe disease is a rare inheritable muscle disorder for which enzyme replacement therapy (ERT) has been available since 2006. Uniform criteria for starting and stopping ERT in adult patients were developed and reported here.

METHODS

Three consensus meetings were organized through the European Pompe Consortium, a network of experts from 11 European countries in the field of Pompe disease. A systematic review of the literature was undertaken to determine the effectiveness of ERT in adult patients on a range of clinical outcome measures and quality of life. A narrative synthesis is presented.

RESULTS

Consensus was reached on how the diagnosis of Pompe disease should be confirmed, when treatment should be started, reasons for stopping treatment and the use of ERT during pregnancy. This was based on expert opinion and supported by the literature. One clinical trial and 43 observational studies, covering a total of 586 individual adult patients, provided evidence of a beneficial effect of ERT at group level. At individual patient level, the response to treatment varied, but factors associated with a patient's response to ERT were not described in many studies. Eleven observational studies focused on more severely affected patients, suggesting that ERT can also be beneficial in these patients. There are no studies on the effects of ERT in pre-symptomatic patients.

CONCLUSIONS

This is the first European consensus recommendation for starting and stopping ERT in adult patients with Pompe disease, based on the extensive experience of experts from different countries.

The influence of a polymorphism in the gene encoding angiotensin converting enzyme (ACE) on treatment outcomes in late-onset Pompe patients receiving alglucosidase alfa

Correlations between angiotensin-converting enzyme (ACE) genotype (I/I, I/D, D/D), disease severity at baseline and response to enzyme replacement therapy (ERT) were assessed in the Pompe disease Late-Onset Treatment Study (LOTS). No correlations were observed between ACE genotype and disease severity at baseline. However, D/D patients appeared to have a reduced response to alglucosidase alfa treatment than I/I or I/D patients, suggesting that ACE polymorphisms may influence the response to alglucosidase alfa treatment and warrants further investigation.

Should patients with asymptomatic pompe disease be treated? A nationwide study in France

INTRODUCTION

Acid α-glucosidase deficiency, that is, Pompe disease, is a glycogenosis for which enzyme replacement therapy (ERT) is available. It is not known whether patients diagnosed at an asymptomatic stage should be treated to prevent progression of the disease.

METHODS

We investigated 7 patients with asymptomatic Pompe disease identified from the French Pompe registry.

RESULTS

The patients had a mean age of 45 (range 24-75) years, a median follow-up duration of 2 (range 1-22) years, and normal clinical examination, pulmonary function tests (PFTs), and echocardiography. All presented with at least 1 subclinical abnormality, including hyperCKemia, vacuolar myopathy, and muscle MRI abnormalities, suggesting that subclinical myopathy was present in all cases.

CONCLUSIONS

Asymptomatic Pompe disease may remain clinically silent for decades, and affected patients should be monitored closely for overt myopathy using clinical examination, PFTs, and muscle MRI to determine when to start ERT.

Simple Method to Genotype the ACTN3 r577x Polymorphism

The alpha-actinin-3 r577x polymorphism (rs1815739) is one of the most important polymorphisms associated with athletic performance. This single-nucleotide mutation leads to a premature stop codon, resulting in a nonfunctional protein product. The presence of the dominant R allele is associated with full power skeletal muscle contraction. Homozygosity for the X allele is correlated with more efficient energy disposure. Restriction fragment length polymorphism and real-time polymerase chain reaction (PCR) are the standard methods used to genotype this polymorphism, but they are expensive and require special equipments. Here, we present a simple and cost-efficient method to genotype the ACTN3 r577x polymorphism by a single PCR. External primers yield a 690-bp product that indicates the template quality. Internal primers produce a 413-bp product if the R allele is present and a 318-bp product if the X allele is present. Our four-primer genotyping PCR was validated by the standard real-time PCR, generally used to genotype this single-nucleotide polymorphism, demonstrating the accuracy of this method. This protocol is perfect for small- or large-scale cohort genotyping of the ACTN3 r577x polymorphism.

Phenotypical variation within 22 families with Pompe disease

Background

Pompe disease has a broad clinical spectrum, in which the phenotype is partially explained by the genotype. The aim of this study was to describe phenotypical variation among siblings with non-classic Pompe disease. We hypothesized that siblings and families with the same genotype share more similar phenotypes than the total population of non-classic Pompe patients, and that this might reveal genotype-phenotype correlations.

Methods

We identified all Dutch families in which two or three siblings were diagnosed with Pompe disease and described genotype, acid α-glucosidase activity, age at symptom onset, presenting symptoms, specific clinical features, mobility and ventilator dependency.

Results

We identified 22 families comprising two or three siblings. All carried the most common mutation c.-32-13 T > G in combination with another pathogenic mutation. The median age at symptom onset was 33 years (range 1–62 years). Within sibships symptom onset was either in childhood or in adulthood. The median variation in symptom onset between siblings was nine years (range 0–31 years). Presenting symptoms were similar across siblings in 14 out of 22 families. Limb girdle weakness was most frequently reported. In some families ptosis or bulbar weakness were present in all siblings. A large variation in disease severity (based on wheelchair/ventilator dependency) was observed in 11 families. This variation did not always result from a difference in duration of the disease since a third of the less affected siblings had a longer course of the disease. Enzyme activity could not explain this variation either. In most families male patients were more severely affected. Finally, symptom onset varied substantially in twelve families despite the same GAA genotype.

Conclusion

In most families with non-classic Pompe disease siblings share a similar phenotype regarding symptom onset, presenting symptoms and specific clinical features. However, in some families the course and severity of disease varied substantially. This phenotypical variation was also observed in families with identical GAA genotypes. The commonalities and differences indicate that besides genotype, other factors such as epigenetic and environmental effects influence the clinical presentation and disease course.